JP4522201B2 - Power supply circuit and motor drive circuit - Google Patents

Description

  The present invention relates to a power supply circuit including a booster circuit, and a motor drive circuit supplied with a boosted power supply voltage from the power supply circuit.

  In general, a booster circuit is widely used in a power supply circuit, a drive circuit, and the like in a semiconductor integrated circuit. FIG. 2 is a circuit diagram showing a motor drive circuit using a booster circuit. Reference numeral 10 denotes a forward / reverse motor driver, in which motor-driving MOS transistors Q1 and Q4 connected in series and motor-driving MOS transistors Q3 and Q2 connected in series are arranged in pairs, and their connection points A coil 11 is connected between the two. The battery voltage VM from the battery 12 is supplied to the common drain of Q1 and Q3, and the common source of Q2 and Q4 is grounded.

  In this forward / reverse motor driver 10, when Q1 and Q2 are on and Q3 and Q4 are off, the first drive current I1 flows through Q1, the drive coils 11 and Q2, and conversely Q1 and Q2 are off, Q3 and When Q4 is on, the motor is driven by the second drive current I2 flowing through Q3 and the drive coils 11 and Q4.

  A large current value of several amperes is required as the first and second drive currents I1 and I2. Therefore, in addition to Q2 and Q4, Q1 and Q3 are also configured as an N-channel type, and the high level of the control voltage applied to the gates of Q1 and Q3 is higher than the battery voltage VM, so that Q1, A method of turning on Q3 with low impedance is employed. In this way, the transistor size can be reduced as compared with the case where Q1 and Q3 are configured as a P-channel type.

  In order to obtain such a high control voltage, the control signal from the control circuit 13 supplied with the first power supply voltage Vdd is level-shifted by the level shift circuit 14 to a high-voltage control signal, Applied to the gate of Q1. Similarly, a level-shifted control signal is applied to the gate of Q3. In addition, a control signal not level-shifted from another control circuit (not shown) to which the first power supply voltage Vdd is supplied is applied to the gates of Q2 and Q4. The output voltage VG of the booster circuit 20 is supplied as the second power supply voltage on the high voltage side of the level shift circuit 14. A smoothing capacitor 22 is connected between the output terminal 21 of the booster circuit 20 and the ground voltage.

The booster circuit 20 outputs, for example, 2Vdd (may be VM + Vdd) as the output voltage VG. Therefore, the high level output of the level shift circuit 14 is VG (= 2Vdd), and the low level output is the ground voltage (0 V). Since VG (= 2Vdd) is set larger than VM, Q1 and Q3 of the forward / reverse motor driver 10 can be turned on with low impedance.
JP 2000-33006 A

  In the motor drive circuit described above, when the first power supply voltage Vdd, which is the main power supply of the circuit, is lowered or shut off (that is, when it becomes 0 V), it is determined that the state is abnormal, and forward and backward It is necessary to stop the operation of the motor driver 10 and stop driving the motor.

  The operation of the booster circuit 30 is also stopped when the first power supply voltage Vdd is lowered or cut off. However, since charges are accumulated in the smoothing capacitor 22 connected to the output terminal 21, the boosted output voltage VG remains as it is. Will do. For this reason, the forward / reverse motor driver 10 may malfunction.

  The mechanism of the malfunction is as follows. The control voltage output from the control circuit 13 becomes unstable due to the decrease or interruption of the first power supply voltage Vdd. Then, the output of the level shift circuit 14 becomes unstable, and VG (= 2Vdd) may be output from the level shift circuit 14, and unnecessary driving current is generated by turning on Q1 and Q2 of the forward / reverse motor driver 10. It will flow.

Therefore, a power supply circuit of the present invention boosts a first power supply voltage to generate a second power supply voltage, a smoothing capacitor connected to an output terminal of the booster circuit, and supplies the booster circuit to the booster circuit. And a discharge circuit that discharges the charge accumulated in the smoothing capacitor when the detection circuit detects a drop in the first power supply voltage. The discharge circuit includes a resistor connected in series between the output terminal and a ground voltage, a control MOS transistor to which a detection signal of the detection circuit is applied to a gate, and the output terminal and the ground voltage. And a discharge MOS transistor having a drain voltage of the control MOS transistor applied to the gate of the control MOS transistor .

  The motor drive circuit of the present invention includes a booster circuit that boosts the first power supply voltage to generate a second power supply voltage, a smoothing capacitor connected to the output terminal of the booster circuit, and the booster circuit. A detection circuit for detecting a decrease in the first power supply voltage to be supplied; and a discharge circuit for discharging the charge accumulated in the smoothing capacitor when the detection circuit detects a decrease in the first power supply voltage; A motor driving MOS transistor, a level shift circuit that controls switching of the motor driving MOS transistor, and a second power supply voltage that is an output voltage of the booster circuit is supplied as a power supply voltage, and a first power supply voltage is And a control circuit for supplying a control voltage to the level shift circuit.

  According to the power supply circuit of the present invention, when a drop in the first power supply voltage is detected, the charge accumulated in the smoothing capacitor is discharged by the discharge circuit, so that the malfunction of the circuit to which the output voltage of the power supply circuit is supplied Can be prevented.

  Further, according to the motor drive circuit, when the first power supply voltage drop is detected, the charge accumulated in the smoothing capacitor is discharged by the discharge circuit, so the power supply voltage of the level shift circuit is also lowered, and the motor drive The MOS transistor is prevented from turning on. This prevents malfunction of the motor drive circuit when the first power supply voltage is lowered or shut off.

  Next, a power supply circuit and a motor drive circuit according to an embodiment of the present invention will be described with reference to FIG. In FIG. 1, a power supply circuit 1 is a circuit that generates an output voltage VG obtained by boosting a first power supply voltage Vdd and supplies the output voltage VG as a second power supply voltage to the level shift circuit 14 of the motor drive circuit. From the charge pump type booster circuit 20A, the smoothing capacitor 22 connected between the output terminal 21 of the booster circuit 20A and the ground voltage, the detection circuit 25 for detecting a decrease in the first power supply voltage Vdd, and the detection circuit 25 The discharge circuit 26 discharges the electric charge accumulated in the smoothing capacitor 22 in accordance with the detection signal. The other circuit configuration is the same as that of the circuit of FIG.

  The charge pump type booster circuit 20A includes a first charge transfer MOS transistor Q5 to which a first power supply voltage Vdd is applied, and a second charge connected in series to the first charge transfer MOS transistor Q5. The transfer MOS transistor Q6, the boost capacitor 23 having a first terminal connected to the connection point of the first charge transfer MOS transistor Q5 and the second charge transfer MOS transistor Q6, and the second of the boost capacitor 23 And a clock driver 24 for supplying the clock CLK to the terminal. The power supply voltage on the high voltage side of the clock driver 24 is the first power supply voltage Vdd.

  The operation of the booster circuit 20A is as follows. When the clock CLK is at a low level (0 V), Q5 is turned on, Q6 is turned off, and the boosting capacitor 23 is charged to Vdd through Q5. When the clock CLK is at a high level (Vdd), Q5 is turned off and Q6 is turned on. Then, due to the capacitive coupling effect of the boosting capacitor 23, the voltage at the connection point between Q5 and Q6 transitions from Vdd to 2Vdd, and an output voltage VG of 2Vdd is obtained through Q6.

  Further, the discharge circuit 26 includes a resistor R1 and a control MOS transistor Q7 having a high resistance value connected in series between the output terminal 21 of the booster circuit 20A and the ground voltage, and between the output terminal 21 and the ground voltage. Are connected in series with a resistor R2 and a discharging MOS transistor Q8. The detection signal VDET of the detection circuit 25 is applied to the gate of the control MOS transistor Q7, and the drain voltage Vd of the control MOS transistor Q7 is applied to the gate of the discharge MOS transistor Q8. Q7 and Q8 are both N-channel types.

  Next, the operation of the circuit described above will be described. When the first power supply voltage Vdd is in a predetermined normal voltage range (for example, 4.5V to 5.5V), the booster circuit 20A operates normally, and the output voltage VG (2Vdd) is obtained and its output The voltage VG is supplied as the power supply voltage for the level shift circuit 14. At this time, the detection signal VDET of the detection circuit 25 is at the high level (Vdd), Q7 is turned on, and the gate of Q8 becomes the ground voltage (0 V), so Q8 is turned off. Accordingly, at this time, the electric charge of the smoothing capacitor 22 is not discharged.

  The control voltage from the control circuit 13 is level-shifted by the level shift circuit 14 and then applied to the gate of the motor driving MOS transistor Q1 of the forward / reverse motor driver. When the output of the level shift circuit 14 is at a high level (2 Vdd), the motor driving MOS transistor Q1 is turned on with a low impedance.

  On the other hand, when the first power supply voltage Vdd falls from a predetermined normal voltage range (for example, when the voltage drops to 2.5 V or less, which is half of 5.0 V), or is cut off (when it drops to 0 V). The booster circuit 20A stops operating. At this time, the first power supply voltage Vdd supplied to the detection circuit 25 is also reduced, but a low level (0 V) is output as the detection signal VDET. Accordingly, Q7 is turned off, and the gate of Q8 becomes the output voltage VG (2Vdd), so that Q8 is turned on. Thereby, the electric charge of the smoothing capacitor 22 is discharged. The smoothing capacitor 22 is discharged until the gate voltage of Q8 equal to the output voltage VG is lowered to the threshold voltage Vt, so that the output voltage VG can be sufficiently lowered.

  Thereby, when the first power supply voltage Vdd is lowered from a predetermined normal voltage range, the output voltage VG of the booster circuit 20A is also sufficiently lowered, so that the power supply voltage of the level shift circuit 14 is also sufficiently lowered, and the control is performed. Even if the control voltage of the circuit 13 becomes unstable, the motor driving MOS transistor Q1 of the forward / reverse motor driver is prevented from being turned on, and malfunction of the motor driving circuit is prevented.

  Although the booster circuit 20A uses a charge pump system, the present invention is not limited to this, and another booster system (for example, a switched capacitor system DC-DC converter) may be used, and the output voltage is limited to 2 Vdd. I can't.

It is a circuit diagram of the power supply circuit and motor drive circuit of this invention. It is a circuit diagram of the motor drive circuit of a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Forward / reverse motor driver 11 Drive coil 12 Battery 13 Control circuit 14 Level shift circuit 20A Booster circuit 21 Output terminal 22 Smoothing capacitor 23 Booster capacitor 24 Clock driver 25 Detection circuit 26 Discharge circuit

Claims (5)

A booster circuit that boosts the first power supply voltage to generate a second power supply voltage, a smoothing capacitor connected to the output terminal of the booster circuit, and a decrease in the first power supply voltage supplied to the booster circuit And a discharge circuit for discharging the charge accumulated in the smoothing capacitor when the detection circuit detects a decrease in the first power supply voltage ,
The discharge circuit includes a resistor connected in series between the output terminal and a ground voltage, a control MOS transistor to which a detection signal of the detection circuit is applied to a gate, and the output terminal and the ground voltage. And a discharge MOS transistor having a drain voltage applied to the gate of the control MOS transistor . The booster circuit includes: a first charge transfer MOS transistor to which the first power supply voltage is applied; a second charge transfer MOS transistor connected in series to the first charge transfer MOS transistor; 2. The power supply circuit according to claim 1, further comprising a clock driver that supplies a clock to a connection point between the first charge transfer MOS transistor and the second charge transfer MOS transistor via a boosting capacitor. . A booster circuit that boosts the first power supply voltage to generate a second power supply voltage, a smoothing capacitor connected to the output terminal of the booster circuit, and a decrease in the first power supply voltage supplied to the booster circuit , A discharge circuit for discharging the charge accumulated in the smoothing capacitor when the detection circuit detects a decrease in the first power supply voltage, a motor driving MOS transistor, and the motor driving A level shift circuit that controls the switching of the MOS transistor and is supplied with the second power supply voltage as a power supply voltage; and a control circuit that is supplied with the first power supply voltage and supplies the control voltage to the level shift circuit. A motor drive circuit characterized by that. The discharge circuit is connected between a resistor connected between the output terminal and a ground voltage, a control MOS transistor to which a detection signal of the detection circuit is applied to a gate, and the output terminal and the ground voltage. 4. The motor drive circuit according to claim 3 , further comprising: a discharge MOS transistor in which a drain voltage of the control MOS transistor is applied to a gate. The booster circuit includes a first charge transfer MOS transistor to which the input voltage is applied, a second charge transfer MOS transistor connected in series to the first charge transfer MOS transistor, and the first charge transfer MOS transistor. 4. The motor drive circuit according to claim 3 , further comprising: a clock driver that supplies a clock to a connection point between the second charge transfer MOS transistor and the second charge transfer MOS transistor via a boosting capacitor.